August 12, 2012, 07:08 AM | #1 |
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boat tail VS flat base ?
I have read that flat base bullets are more accurate at 100 yds or less and boat tails are more accurate at over 100 yds. I am in the process of hand loading both to see for myself if this is true.
At what ranges do you guys prefer flat base or boat tails ? |
August 12, 2012, 07:51 AM | #2 | |
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http://thefiringline.com/forums/show...83#post5111383
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That was easy to find, from two months ago.
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August 12, 2012, 03:33 PM | #3 |
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Rebs:
Both flat base an boat tails have equil accuracy regardless of the range that they are shot at. The advantage that the boat tail has it when it drops to sub sonic velocity: the air folds around the boat tail and gives the bullet a push increasing the range slightly. That said, I prefer boat tails because of their looks and ease of bulllet seating. There is nothing prettier than a 300 grain, .375 H&H Sierra boat tail. Semper Fi. Gunnery Sergeant Clifford L. Hughes USMC Retired |
August 12, 2012, 04:23 PM | #4 |
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Sierra Bullets published some info on bullet base accuracy years ago in their reloading manuals. Their first ballistic tech's told me the same stuff many times.
In their super perfect test barrels used to check bullets for accuracy, boattailed bullets shot more accurate than flat based ones. In sporting and military rifles testing reloads for accuracy as well as other data for publishing in their manuals, 'twas the other way around; flat based ones shot the most accurate. This was at their 100-yard range in California before moving to Missouri. Addendum....... Old Ropers post below is probably valid. I know that the quality of custom small caliber boattails has improved over the years. It's no surprise that BT's are as accurate as they are. Probably 'cause they're more perfectly balanced from near zero tolerance in jacket thickness as well as jacket and core metalurgy uniformity caused by the density of the metals used. Last edited by Bart B.; August 13, 2012 at 07:53 AM. |
August 12, 2012, 05:03 PM | #5 |
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This year at the BR Super Shoot L Hottenstein BT bullet won more placing in the top 40 light/heavy agg at 100/200 than any other bullet that other shooters could buy.
Bart's been making a winning BT http://www.bartsbullets.com/products....html#Boattail Of the total top 40 shooters almost 1/3 build their own rifles and make their own bullets. One of the problems comparing BR style bullets is the average shooter is not going to build or have rifle twisted for the BR style bullets or even throated for them.
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August 12, 2012, 11:50 PM | #6 |
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A bullet isnt going to be less accurate at 100 yards than it is a 300 yards.... There is no way a bullet that gives 3 moa groups at 100 yards is going to give 1 moa groups at 300 yards..... A bullet isnt going to "stabilize" once it gets past 100 yards and become more accurate. If its unstable from 0 to 100 yards, its more likley than not already way off target, and even if it did magically "stabilize and fly straight" at 100 yards its already pointed in the wrong direction from being unstable out to 100 yards... see the problem here?
People have some weird thoughts about guns.... I had to explain to my little brother that a bullet doesnt need 50-100 yards to "get up to speed" (as he put it) after you shoot it.... Its going as fast as its ever going to go when it leaves the muzzle... And he is in the army!!!! My guess on this one (bt vs flat base) is someone heard someone say something like "at 100 yards there is no point in using boat-tail's since their advantage doesnt show till 200-300 yards" or "you are wasting your money using boat tail bullets at 100 yards, you should use flat base", and later when they regurgitated it, it became "flat base is more accurate at 100 yards than boat-tails, but boat-tails are more accurate further out".... and then spread from there.... |
August 13, 2012, 06:56 AM | #7 | |
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August 13, 2012, 08:23 AM | #8 |
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Rebs, I just saw your other post on FB vs FT bullets
http://thefiringline.com/forums/showthread.php?t=492616
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August 13, 2012, 05:13 PM | #9 |
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There are a few things to remember when choosing FBs and BTs.
1- A FB will "leak" less gas, especially in a BR barrel when the bullet is seated so as to jam* in the lands. Less leakage means less turbulence ahead of the bullet, both in the barrel and at the muzzle, which can result in an easier tune and possibly a wider tuning node, which will make accuracy easier to attain. If all that means nothing to you, don't be alarmed-- it probably means nothing to your particular application--much like the entire controversy of BT vs. FB in the first place. 2- A BT bullet is a better flier once beyond the range in which pitch and yaw are more important than wind bucking and true ballistic performance. That might sound complicated, but it is really not. You can prove the principle that created BT and rebated BT bullets yourself with a Frisbee or a football. If you throw either one, especially thrown when hard as you can, and observe their flight, you will notice that at first, they tend to flail around somewhat, but later in flight settle down to a smooth trajectory. This is a good part of the idea behind a BT bullet. A bullet meant to fly only a few hundred yards does not need to smooth out its flight, but will benefit greatly in accuracy when the tune of the barrel is such that it does not impart a bigger built in "wobble" to the bullet. 3- Bullet diameter and start pressure along with seating depth can affect the effect of gas leakage. I have bought custom made 6mm BR bullets from makers who tell me that there is no appreciable difference in group size between their FB and BT bullets. As far as I can tell they are both right and wrong in this belief. In my 6mmPPC there does not seem to be any difference that I can see in a FB or a BT bullet when you go by group size--always subtracting the "pilot error" induced by the shooter--But-- in my 6mmBR Norma (much hotter powder charge) and my .243(6mm) WSSM (much much hotter powder charge) there seems to be a bigger difference than I can account for because of tune or recoil. In my 22 BR there seems to be such a small bevel in the BT that it makes no difference that I can see. Same goes for the .223 Rem. Same goes for the .30-06, but not for the .30BR, for some reason-- I think maybe because of the very fast powder used in that cartridge? This all applies to ranges of 300 yards or less. I have not shot a FB bullet beyond that range, and now it is too late for me to do that experiment since I can't drive as far as the closest longer range facility. * Jam is a BR technique that is safe and works well in custom made barrels when you know the exact measurements of your chamber and brass and can control the neck thickness and diameter of your brass reliably.
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August 13, 2012, 05:47 PM | #10 |
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Plus 1 to what Clark said.
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August 13, 2012, 07:02 PM | #11 |
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amamnn, how do you determine the "gas leak" difference between boattail and flat base bullets?
Do you somehow measure it? If so, with what? Surely you're not making assumptions....... All the footballs I've seen in flight have the same point nutation circles about their trajectory axis at both ends throughout their flight. http://electron9.phys.utk.edu/balls/ballinflight.asp |
August 13, 2012, 08:05 PM | #12 | |
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The Frisbee/football analogy above seems to make sense, but really it doesn't. The reason a Frisbee or football wobbles as you throw it, is because you didnt throw it perfectly. Then, as it flies aerodynamic drag will cause it to fly in the most efficient way possible, which is without wobbling. Its not that the football gets "more accurate" as it flies, thats simply not possible. If its off target at close range, its going to be off target at long range. Same with bullets. Even though its wobbling right after you throw it, its still on its way to its target. If you throw it really badly, the wobble will stay with it all the way, if you throw it pretty good the wobble goes away. Its simply conservation of energy, nothing more. SO why the myth? It comes from a lack of understanding the relationship between MOA and BC. Well, as we know, different guns will always shoot better with certain bullets shot at certain velocities. The key to load development is to find the velocity that the bullet you want to use shoots best at. If you take a random boat tail bullet and a random flat base bullet of the same weight and shoot them both at the same velocity, if your guns happens to shoot the FB bullet better at that velocity, its easy to make the mistake of thinking that the FB bullet shoots better at short range, while the BT bullet shoots better at long range. WHY? Because a Flat base bullets groups will open up faster at range than a boat tail, especialy in the wind, due to its high B.C. (the bt's) In fact, its easy to make a neat little chart showing how a FB bullet is more accurate at short ranges and a BT bullet is more accurate at long ranges, without having to fudge the data at all. All you have to do is select a FB bullet that starts out with smaller groups than the BT bullet at short range. Because the BT bullet has a higher BC, its going to have less wind drift down range, so shot side by side, even if the FB bullet STARTS with smaller groups, the BT will eventually have smaller groups once the range gets out there, even if the difference in short range groups is fairly dramatic, because its (the BT) more aerodynamic. SO for example, start with a FB bullet that groups at 1/2" at 100 yards, and a BT bullet that groups at 1".The FB bullet is twice as accurate as the BT bullet. Out to 200-300 yards, the advantage the boat-tail has in bucking the wind doesnt have time to show so the FB bullets groups will still be smaller than the BT groups. But once you get past 200-300 yards, the BT bullet groups will start to get smaller than the FB bullet groups. The key to remember here, is that its NOT that the BT bullets are getting more accurate, with range. thats simply not possible, Whats happening is that the FB bullets are getting LESSaccurate, due to its lower B/C, the wind will affect it more and more as distance gets greater and greater. Its easy to see this by simply calculating the MOA at each range shot. What you will NOT see is the BT bullet shooting 2moa at 100 yards, then suddenly shrinking to 1moa at 400 yards. What will happen is that the MOA of BOTH FB and BT bullets is going to increase with range, but the FB will increase faster. It can easily give the illusion that the FB is better at short range and the BT is better at long range, but thats all it is, an illusion created by bullet selection. Start with two bullets that are equally accurate at short range, and you will see the difference in groups between the BT and FB bullets increase even more dramatically than it did in the test where the FB bullet started out more accurate.... So to recap, If you start with a FB bullet thats more accurate than the BT, then OF COURSE the FB bullet will be better at short range, becase it shoots better out of YOUR gun. Then as range increases, the more arodynamic BT bullet will eventualy end up with smaller groups than the FB. But its not because the BT is getting more accurate with range. Its because the FB is getting LESS accurate. So yes, if a FB bullet shoots really well for you and you only shoot to 200 yards, then you would be wasting your money buying a boat tail bullet that shoots just as well at 200 yards. Thats just commons sense...... But, that doesnt mean the FB bullet is inherently more accurate simply by virture of being a FB bullet. Its just means that that particular FB bullet shoots really well out of your gun, and you dont shoot at long enough range for the disadvantages of a FB bullet to affect your groups. Its certainly possible that its easier to find an accurate load with FB bullets, but its simply not true that BT bullets start out less accurate, then get more accurate later on down the line. They simply are less affected by wind. Again, its not that BT bullets get MORE accurate at long range, its that FB bullets get LESS accurate at range. |
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August 13, 2012, 08:24 PM | #13 |
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DACAUR--- Your last statement pretty much sums it all up. Hit the nail on the head so to say.
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August 13, 2012, 08:26 PM | #14 |
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"The advantage that the boat tail has it when it drops to sub sonic velocity: the air folds around the boat tail and gives the bullet a push increasing the range slightly."
Sorry but internet misinformation... T. |
August 13, 2012, 10:27 PM | #15 | |
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Dacur's claim:
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I'll never be convinced that two bullet types, one flat based and the other boattailed, that are perfect in shape and balance, even with different weights but with muzzle velocities having zero fps spread and fired in stable and identical atmospheric conditions, one will be more accurate than the other. One's trajectory path will be greater than the other, but both will be very repeatable so accuracy will be the same with each. |
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August 13, 2012, 10:45 PM | #16 |
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Bart B. -- i think you're right in a theoretical sense. But it's the sense in which it's only true in an unrealistic situation. There are yet more factors, such as barrel whip and harmonics that (in the real world) are impossible to eliminate as variables. One bullet may perform better in one real-world barrel than another and the other way around with a different barrel for inscrutable reasons.
There's also the transonic barrier, which has only been alluded to so far. The BT will stay supersonic longer than the FB, which should be a little significant as long as our thought experiment still includes an atmosphere. Sent from my DROID4 using Tapatalk 2 |
August 14, 2012, 05:00 AM | #17 |
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jephthai, there are range conditions when there's no wind; a realistic situation. How else could someone shoot a dozen or more 10-shot groups at 600 yards and all are under 1.5 inches. That's been done, albiet with boattail bullets.
Barrels whip at the same frequency (and therefore, the multiples thereof which are its harmonics) for every shot fired. It's metalurgy properties defining its rigidity (or stiffness) don't change with bullets, nor velocity for that matter. And I don't think anyone's talking about longer ranges when bullets have gone subsonic; they all change trajectory paths to some degree when they transcend the sound barrier. Higher BC bullets leaving at the same velocity do it later in their flight. |
August 14, 2012, 06:15 AM | #18 |
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Thank you guys for all the replies, I am sure getting an education on this thread. I appreciate it.
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August 14, 2012, 06:53 AM | #19 | ||
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I would argue that such performance is a feat of wind reading, not bullet performance in lucky conditions. Heck, i could do it with my kit if i had a brain to read the wind . I'm pretty sure that 'no wind' occurs very rarely across a 600 yard distance. Quote:
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August 14, 2012, 07:44 AM | #20 | ||
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jephthai mentions:
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August 14, 2012, 01:43 PM | #21 | |
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Am I crazy? Sent from my DROID4 using Tapatalk 2 |
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August 14, 2012, 02:03 PM | #22 |
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"I have read that flat base bullets are more accurate at 100 yds or less and boat tails are more accurate at over 100 yds. "
Anyone telling you anything about accuracy before it's tested in individual rifles and loads will probably lie to you about other stuff too. |
August 14, 2012, 03:09 PM | #23 |
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jephthai, yes, bullets with different bearing surfaces will probably exit at different places in the barrel's whip cycle. But the difference between the two won't be significant. At .30-06 muzzle velocities, it takes about 2.5 milliseconds for a bullet to go from case mouth to out the muzzle. A few millionths second either side ain't all that important. I've shot bullets from 168 grains through 220 grains in the same barrel, each easily holding 1/2 MOA at 300 yards at muzzle velocities from 2700 down to 2400 fps. I know they're not all leaving at the same place in the barrel's whip cycle. And shot 190, 200 and 220 grain bullets from a 30 caliber magnum barrel that all shot about 1/2 to 5/8 MOA at 1000 yards; they leave at different places, too.
Regarding the "node" of a whipping barrel, that's when it's straight out without any bending. The "antinode" is when the barrel's bent the most. Best accuracy typically happens when bullets leave just before the "antinode" so slower ones leave at higher muzzle axis angles and 'cause the drop more way down range, that's compensated for. Some folks "tune" their barrels with a weight on them so best accuracy happens in some range band some distance away. jephthai, you're not crazy. You're thinking. And asking good questions; a sign of intelligence. Bless you. |
August 14, 2012, 03:17 PM | #24 | |
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The low pressure area behind a bullet "drags" on it going through the air. 'Tis like a vacuum trying to suck the bullet back into it. Hence the exterior ballistic terms "low drag" meaning a bullet with that characteristic slows down less in flight. The word's also used for "drag function" which is part of ballistic formulas used to calculate trajectories for a bullet's ballistic coefficient. |
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August 14, 2012, 06:11 PM | #25 | |
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Again, the BT bullet isnt somehow magically more accurate at longer ranges than it is at shorter ranges. The FB bullet is simply LESS accurate to a greater degree at long range vs short range than the BT..... |
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